Growth Of InAs Nanowires Research Articles

High-density and high-uniformity InAs quantum nanowires on Si(111) substrates

InAs nanowires (NWs) were grown on SiOx pinholes formed on Si(111) substrates by molecular beam epitaxy. Influences of electron-beam (EB) irradiation on the SiOx layer on the pinhole formation and the subsequent InAs NW growth were studied. As the EB irradiation dose increased, the pinhole density in the SiOx layer decreased. From atomic force microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy results, it was found that the pinhole etching of the SiOx layer by Ga droplets was suppressed by carbon adsorption due to the EB irradiation. By forming high-density pinholes on the SiOx layer without the EB irradiation, high-density InAs NWs with 1–2 × 1010 cm−2 were grown successfully, and the uniformity in the NW diameter improved. The standard deviation of the NW diameter was 1.8 nm (8.8%) for high-density NWs. In addition, the NW diameter decreased with decreasing EB dose, and the NW diameter was controlled by adjusting the diameter of Ga droplets forming the pinholes. As the NW diameter decreased, photoluminescence spectra of the NWs shifted to higher energies than the bandgap energy of the wurtzite InAs bulk. From these results, we successfully fabricated high-density and high-uniformity InAs NWs with quantum size effects on EB-unirradiated SiOx/Si(111).

Large-area epitaxial growth of InAs nanowires and thin films on hexagonal boron nitride by metal organic chemical vapor deposition

Large-area epitaxial growth of III–V nanowires and thin films on van der Waals substrates is key to developing flexible optoelectronic devices. In our study, large-area InAs nanowires and planar structures are grown on hexagonal boron nitride templates using metal organic chemical vapor deposition method without any catalyst or pre-treatments. The effect of basic growth parameters on nanowire yield and thin film morphology is investigated. Under optimised growth conditions, a high nanowire density of 2.1 109 cm−2 is achieved. A novel growth strategy to achieve uniform InAs thin film on h-BN/SiO2/Si substrate is introduced. The approach involves controlling the growth process to suppress the nucleation and growth of InAs nanowires, while promoting the radial growth of nano-islands formed on the h-BN surface. A uniform polycrystalline InAs thin film is thus obtained over a large area with a dominant zinc-blende phase. The film exhibits near-band-edge emission at room temperature and a relatively high Hall mobility of 399 cm−2/(Vs). This work suggests a promising path for the direct growth of large-area, low-temperature III–V thin films on van der Waals substrates.

Morphology Transition of Te-Doped InAs Nanowire on InP(111)B Grown Using MOCVD Method

In this paper, we reported changes in the growth morphology of n+InAs nanowires (NWs) doped with Te which were selectively grown on nano-hole patterned InP(111)B substrates using an MOCVD method. While the vertical growth of InAs NWs in the <111> direction was extremely suppressed, their lateral growth was enhanced when the diethyl-tellurium (DETe) flow rate was increased as they grew. Moreover, the sidewall planes evolved from (11¯0) (90° against the (111) plane) to a reverse-tapered morphology, which had a 62° slope against the InP (111)B plane, when the Te flow rate and growth time were increased. This indicates that the surfactant effect of adsorbed Te atoms on InAs changes the relative growth rate between (111) and (11¯0) due to the increase in surface free energy in the growth plane.

New growth mechanism of InAs nanowires array in selective-area growth by MOCVD

Traditional view on the growth mechanism of InAs nanowires (NWs) arrays in selective-area growth (SAG) holds that the growth of InAs NWs is based on the catalyst-free mechanism of faceting growth dominantly. Here, based on analyses and comparisons between the InAs NWs in unselective-area growth (USAG) on bare Si substrates and the InAs NWs arrays in SAG, we put forwards a new point of view that the growth mechanism of InAs NWs arrays in SAG is self-catalyzed vapor–liquid–solid (VLS) mechanism. By designing interrupted growth of InAs NWs in SAG and growth of InAs/GaSb heterostructured NWs in SAG, traces of In droplets were found during SAG of InAs NWs, which directly demonstrate self-catalyzed VLS growth mechanism for the InAs NWs arrays in SAG.

Te-doped selective-area grown InAs nanowires for superconducting hybrid devices

Semiconductor nanowires have emerged as versatile components in superconducting hybrid devices for Majorana physics and quantum computing. The transport properties of nanowires can be tuned either by field effect or doping. We investigated a series of InAs nanowires the conductivity of which has been modified by $n$-type doping using tellurium. In addition to electron microscopy studies, the wires were also examined with atomic probe tomography to obtain information about the local incorporation of Te atoms. It was found that the Te atoms mainly accumulate in the core of the nanowire and at the corners of the {110} side facets. The efficiency of $n$-type doping was also confirmed by transport measurements. As a demonstrator hybrid device, a Josephson junction was fabricated using a nanowire as a weak link. The corresponding measurements showed a clear increase of the critical current with increase of the dopant concentration.

Phase Control Growth of InAs Nanowires by Using Bi Surfactant

To realize practical applications of nanowire-based devices, it is critical, yet challenging, to control crystal structure growth of III-V semiconductor nanowires. Here, we demonstrate that controlled wurtzite and zincblende phases of InAs nanowires can be fabricated using bismuth (Bi) as a surfactant. For this purpose, catalyst free selective area epitaxial growth of InAs nanowires was performed using molecular beam epitaxy (MBE). During the growth, Bi was used which may act as a wetting agent influencing the surface energy at growth plane ends, promoting wurtzite crystal phase growth. For a demonstration, wurtzite and zincblende InAs nanowires were obtained with and without using Bi-flux. Photoluminescence spectroscopy (PL) analysis of the nanowires indicates a strong correlation between wurtzite phase and the Bi-flux. It is observed that the bandgap energy of wurtzite and zincblende nanowires are ∼0.50 eV and ∼0.42 eV, respectively, and agree well with theoretical estimated bandgap of corresponding InAs crystal phases. A blue shift in PL emission peak energy was found with decreasing nanowire diameter. The controlled wurtzite and zincblende crystal phase and its associated heterostructure growth of InAs nanowires on Si may open up new opportunities in bandgap engineering and related device applications integrated on Si. Furthermore, this work also illustrates that Bi as a surfactant could play a dynamic role in the growth mechanism of III-V compound semiconductors.

Semiconductor Epitaxy in Superconducting Templates.

Integration of high-quality semiconductor–superconductor devices into scalable and complementary metal-oxide-semiconductor compatible architectures remains an outstanding challenge, currently hindering their practical implementation. Here, we demonstrate growth of InAs nanowires monolithically integrated on Si inside lateral cavities containing superconducting TiN elements. This technique allows growth of hybrid devices characterized by sharp semiconductor–superconductor interfaces and with alignment along arbitrary crystallographic directions. Electrical characterization at low temperature reveals proximity induced superconductivity in InAs via a transparent interface.

Effect of Flow Rate Scaling on SAE-InAs Crystal Phase and Integration of Self-Catalyzed InAs/InSb Heterostructure Nanowires on Si (111) Substrate by MOCVD

The effect of III-V molar flow scaling on crystal quality of selectively grown InAs nanowires on patterned Si (111) substrate is investigated by metal organic chemical vapor deposition. We found the correlations between molar flow rate scaling and selectivity and InAs crystal structure have been investigated. When the molar flow rate is higher, nanowire follows random nucleation and exhibits zincblende crystal structure, whereas growth selectivity increases to 97% at intermediate molar flow rates and nanowire exhibits wurtzite dominant crystal phase with occasional stacking faults. Once the molar flow rate is scaled-down aggressively, nanowire exhibits polytype crystal structure with small degradation in selectivity. The resistivity calculated from current-voltage curve of moderate molar flow rate InAs nanowires showed 15.9 × 10–3 Ωcm, which was significantly (1.6 times) lower than typical InAs nanowires with low molar flow rate (25.31 × 10–3 Ωcm). Finally, we integrate axial InSb heterostructure nanowire with two different crystal structures on InAs stem by self-catalyzed selective area epitaxy for the V/III ratio of 2. This study further offers good opportunity to tune the crystal structure of InSb with the help of In-catalyzed growth technique.

A comparative study of graphite and silicon as suitable substrates for the self-catalysed growth of InAs nanowires by MBE

In order to fully exploit the enormous potential of functional monolithic nanowire/graphene hybrid structures in high-performance flexible devices, a better understanding of the influence of the graphitic substrate (GS) on NWs growth is crucial. InAs nanowires (NWs) were simultaneously grown on Si and GS with identical growth temperature, In-flux and V/III flux ratio via an In-catalysed growth technique. It is demonstrated that the GS is a more favourable platform for the growth of dense InAs NWs under highly In-rich conditions (low V/III flux ratio), whereas silicon is a more suitable substrate under a highly As-rich condition (high V/III flux ratio). It is shown that the GS enables NWs growth at high In-flux which has enormous potential for the fabrication of cost-effective nanodevices. Transmission electron microscopy analysis of the NW/GS interface confirms the NWs are well aligned on the graphitic substrate. This study opens new possibilities for the choice of suitable substrate for the optimal growth of NWs under various conditions.

A theoretical and experimental study on effect of growth time on self-catalyzed InAs nanowires

We in detail investigated the effect of growth time on InAs nanowires (NWs) grown on Si substrates by metal-organic chemical vapor deposition. It is found that the axial growth of InAs NWs is nonlinear and shows different trends with different NW diameters. Thin NWs grow faster than thick NWs in length, and the radius of both thin and thick NWs have no dependence on growth time. Based on self-catalyzed growth mechanism, we established a kinetic growth process to simulate the growth of InAs NWs on Si. We analyzed some dependences, including length-time, diameter-time and length-diameter dependences. Calculations are in good agreements with experimental ones. It indicates that growth saturation and growth rates of NWs are determined by diffusion length of In adatoms, initial diameter of seed particles and the amount of adatoms per unit area.

Influence of Molecular Beam Epitaxy (MBE) Parameters on Catalyst-Free Growth of InAs Nanowires on Silicon (111) Substrate

The effect of molecular beam epitaxy parameters on catalyst-free growth of InAs nanowires using oxide templates on Si (111) substrate has been studied. Two different approaches, i.e., thermal and plasma-enhanced chemical vapor deposition, were used to prepare the oxide templates. The length, diameter, density, and quality of the nanowires depended strongly on the substrate temperature, As/In beam equivalent pressure ratio, and growth rate, whereas the type, thickness, and uniformity of the oxide were found to affect only the density of the nanowires. Nanowires could be grown effectively in only a very narrow range of these growth parameters. The surface morphological, structural, and optical properties of the nanowires were assessed using various techniques including field-emission scanning electron microscopy, high-resolution x-ray diffraction analysis, transmission electron microscopy, and Raman spectroscopy.

A new insight into the mechanism of low-temperature Au-assisted growth of InAs nanowires

We propose a new insight into the mechanism of low-temperature Au-assisted growth of InAs nanowires. The nanowire MBE growth was achieved at temperature of 270 °C on silicon substrates and was described theoretically via vapor–solid–solid mechanism.

Insight of surface treatments for CMOS compatibility of InAs nanowires

A CMOS compatible process is presented in order to grow self-catalyzed InAs nanowires on silicon by molecular beam epitaxy. The crucial step of this process is a new in-situ surface preparation under hydrogen (gas or plasma) during the substrate degassing combined with an in-situ arsenic annealing prior to growth. Morphological and structural characterizations of the InAs nanowires are presented and growth mechanisms are discussed in detail. The major influence of surface termination is exposed both experimentally and theoretically using statistics on ensemble of nanowires and density functional theory (DFT) calculations. The differences observed between Molecular Beam Epitaxy (MBE) and Metal Organic Vapor Phase Epitaxy (MOVPE) growth of InAs nanowires can be explained by these different surfaces terminations. The transition between a vapor solid (VS) and a vapor liquid solid (VLS) growth mechanism is presented. Optimized growth conditions lead to very high aspect ratio nanowires (up to 50 nm in diameter and 3 micron in length) without passing the 410 °C thermal limit, which makes the whole process CMOS compatible. Overall, our results suggest a new method for surface preparation and a possible tuning of the growth mechanism using different surface terminations.

Growth and Crystal Structure Investigation of InAs/GaSb Heterostructure Nanowires on Si Substrate

We report gold-free growth of vertically aligned InAs/GaSb heterostructure nanowires (NWs) on Si(111) substrate by metal organic chemical vapor deposition technique. The effect of growth temperature on morphology and growth rate for InAs and InAs/GaSb heterostructure NWs were investigated. A combination of high material flow rates and optimum temperature (600 °C) has given better crystal quality of InAs nanowires. The morphology and shell thickness of NWs as observed by scanning electron microscope and transmission electron microscope (TEM) measurements can be tuned by the growth temperature. Electron microscopy also shows the formation of GaSb both in radial and axial directions outside the InAs NW core at certain growth temperatures. Crystal structure of InAs and InAs/GaSb heterostructure NWs was analyzed by high-resolution TEM and fast Fourier transform analysis. Using good crystalline InAs core grown at optimized growth temperature (600 °C), GaSb shell has been grown without any misfit dislocations at the core-shell interface. Basic electrical properties have been measured by forming ohmic contacts. I–V characteristics exhibit linear response indicating good ohmic behavior. These results show good control over InAs NWs growth, the GaSb shell thickness, and its crystal quality, which are essential for future nanoelectronic devices such as tunneling FET.

The effect of Ga pre-deposition on Si (111) surface for InAs nanowire selective area hetero-epitaxy

Vertical InAs nanowires (NWs) grown on a Si substrate are promising building-blocks for next generation vertical gate-all-around transistor fabrication. We investigate the initial stage of InAs NW selective area epitaxy (SAE) on a patterned Si (111) substrate with a focus on the interfacial structures. The direct epitaxy of InAs NWs on a clean Si (111) surface is found to be challenging. The yield of vertical InAs NWs is low, as the SAE is accompanied by high proportions of empty holes, inclined NWs, and irregular blocks. In contrast, it is improved when the NW contains gallium, and the yield of vertical InxGa1-xAs NWs increased with higher Ga content. Meanwhile, unintentional Ga surface contamination on a patterned Si substrate induces high yield vertical InAs NW SAE, which is attributed to a GaAs-like seeding layer formed at the InAs/Si interface. The role of Ga played in the III-V NW nucleation on Si is further discussed. It stabilizes the B-polarity on a non-polar Si (111) surface and enhances the nucleation. Therefore, gallium incorporation on a Si surface is identified as an important enabler for vertical InAs NW growth. A new method for high yield (>99%) vertical InAs NW SAE on Si using an InGaAs nucleation layer is proposed based on this study.

Temperature effect on the growth of Au-free InAs and InAs/GaSb heterostructure nanowires on Si substrate by MOCVD

We demonstrate the growth of vertically aligned Au-free InAs and InAs/GaSb heterostructure nanowires on Si (1 1 1) substrate by Metal Organic Chemical Vapor Deposition (MOCVD). The effect of growth temperature on the morphology and growth rate of the InAs and InAs/GaSb heterostructure nanowires (NWs) is investigated. Control over diameter and length of the InAs NWs and the GaSb shell thickness was achieved by using growth temperature. As the GaSb growth temperature increase, GaSb radial growth rate increases due to the increase in alkyl decomposition at the substrate surface. Diffusivity of the adatoms increases as the GaSb growth temperature increase which results in tapered GaSb shell growth. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) measurements revealed that the morphology and shell thickness can be tuned by the growth temperature. Electron microscopy also shows the formation of GaSb both in radial and axial directions outside the InAs NW core can be controlled by the growth temperature. This study demonstrates the control over InAs NWs growth and the GaSb shell thickness can be achieved through proper growth temperature control, such technique is essential for the growth of nanowire for future nano electronic devices, such as Tunnel FET.

Selective area growth of InAs nanowires from SiO2/Si(1 1 1) templates direct-written by focused helium ion beam technology

We report on the selective area growth of InAs nanowires on patterned SiO2/Si (1 1 1) nano-holes, prepared by focused helium ion beam technology. We used a single spot mode, in which the focused helium ion beam was fixed on a single point with a He+-ion dosage, ranging from 1.5 pC to 8 pC, to drill the nano-holes. The smallest hole diameter achieved is ∼8 nm. We found that low He+-ion dosage is able to facilitate the nucleation of (1 1 1)B InAs on the highly mismatched Si, leading to the vertical growth of InAs nanowires (NWs). High He-ion dosage, on the contrary, severely damaged Si surface, resulting in tilted and stripe-like NWs. In addition to titled NW grown from (1 1 1)A InAs domain, a new titled growth direction due to defect induced twinning was observed. Cross-sectional TEM images of vertical NWs show mixed wurtizite (WZ) and zincblende (ZB) phases, while WZ phase dominants. The stacking faults resulting from the phase change is proportional to NW diameter, suggesting that the critical diameter of phase turning is larger than 110 nm, the maximum diameter of our NWs. Period of misfit dislocation at the InAs/Si interface of vertical NW is also found larger than the theoretical value when the diameter of heterointerface is smaller than 50 nm, indicating that the small contact area is able to accommodate the large lattice and thermal mismatch between InAs and Si.

Influence of growth parameters on In-droplet-assisted growth of InAs nanowires on silicon

The influence of growth parameters on the morphology and density of InAs nanowires (NWs) grown on bare Si substrates using Indium (In) droplets as catalyst is investigated. By tuning the growth temperature, V/III flux ratio, and growth rate, the diameter and yield of as-grown NWs were controllably manipulated. It is demonstrated that the In-droplet-assisted growth of InAs NWs can only be realized on bare Si within a relatively narrow growth window of 420–475 °C. Below 420 °C, NWs’ growth is kinetically limited, while the highest yield of vertically aligned NWs was obtained at ~450 °C. It is shown that In-catalyzed InAs NWs nucleation can only be realized on Si at highly As-rich conditions (V/III flux ratio >50), while the axial growth rate was found to be strongly dependent on the V/III flux ratio. The nucleation and axial growth of In-catalyzed InAs NWs are promoted by a low growth rate, while a high growth rate favors the formation of unwanted parasitic islands.

Tuning growth direction of catalyst-free InAs(Sb) nanowires with indium droplets

The need for indium droplets to initiate self-catalyzed growth of InAs nanowires has been highly debated in the last few years. Here, we report on the use of indium droplets to tune the growth direction of self-catalyzed InAs nanowires. The indium droplets are formed in situ on InAs(Sb) stems. Their position is modified to promote growth in the 〈11–2〉 or equivalent directions. We also show that indium droplets can be used for the fabrication of InSb insertions in InAsSb nanowires. Our results demonstrate that indium droplets can initiate growth of InAs nanostructures as well as provide added flexibility to nanowire growth, enabling the formation of kinks and heterostructures, and offer a new approach in the growth of defect-free crystals.

MBE growth of self-assisted InAs nanowires on graphene

Self-assisted growth of InAs nanowires on graphene by molecular beam epitaxy is reported. Nanowires with diameter of ∼50 nm and aspect ratio of up to 100 were achieved. The morphological and structural properties of the nanowires were carefully studied by changing the substrate from bilayer graphene through buffer layer to quasi-free-standing monolayer graphene. The positional relation of the InAs NWs with the graphene substrate was determined. A 30° orientation configuration of some of the InAs NWs is shown to be related to the surface corrugation of the graphene substrate. InAs NW-based devices for transport measurements were fabricated, and the conductance measurements showed a semi-ballistic behavior. In Josephson junction measurements in the non-linear regime, multiple Andreev reflections were observed, and an inelastic scattering length of about 900 nm was derived.